Anion transport through polymer inclusion membranes facilitated by transition metal containing carriers

New polymer inclusion membrane (PIM) carriers to facilitate membrane transport of anions have been prepared consisting of bis(pyridylmethyl)amine compounds coordinated to transition metal ions (Fe³⁺, Cu²⁺, Zn²⁺). One of the carriers is based on a resorcinarene bonded to four bis(pyridylmethyl)amines. These carriers have been included in cellulose triacetate (CTA) based PIMs to study competitive transport among halides (F^-, Cl^-, Br^-, I^-) and oxoanions (SO₄^2-, SeO₄^2-, NO₃^- and ReO₄^-). Several compounds, tris(2-butoxyethyl) phosphate, dibutyl phthalate and ethylbenzoate, ethyl phthalyl ethyl glycolate and benzoic acid 2-ethoxyethyl ester, were used as plasticizers in the membranes to provide solubility of the metal carrier complexes. Separations were performed with and without antiport anions. Permeabilities of oxoanions increased with the use of 0.05 M KCl as an antiport solution. In some cases, Cl^- was selectively transported over F^-, Br^- and I^- in contradiction to the usual Hoffmeister-based selectivities. Excellent ReO₄^- transport over NO₃^-, SO₄^2- and SeO₄^2- was observed for certain systems. Permselectivity for ReO₄^-/NO₃^- was 312 for a PIM using ethyl phthalyl ethyl glycolate as plasticizer, zinc complex as carrier and an antiport solution of 0.05 M KCl.